543 replies to this topic

[Ptkacik]

What are the differences between a Maksutov Cassegrain (MCT) and a Schmidt Cassegrain (SCT) or any thing else? Is the best way to compare them by starting at price you can afford and target audience of sky goal?

 

1. I get the impression that an SCT is an all around telescope with marginal contrast but light weight, small, and great resolution. Big ones are very good.

 

2. An MCT is higher power tool with an F15 to F20 ratio. Great high power optics.

 

3. In comparison, a refractor is a wide field tool with an F7 ratio and a premium price in Apo format.  5" Apo's can be very nice but pricey.

 

4. I've not looked through one but have the impression that a Maksutov Newtonian is a great visual tool for the price but has the the disadvantage of being very cumbersome and heavy.

 

5. Reflectors, in comparison, are reasonably priced in Dob format, and have great optical performance. They do get very heavy and can be unwieldy on Equatorial mounts.

 

Or can you correct my opinion on this general analysis?

 

Clear skies,

Peter

 

 

 

 

[mt.jennings]

Short focus refractors (as well as Apo's) are a recent development. Classic achromatic refractors are usually f/10 to f/15.  Quality MCT & MNT's are the only designs that rival classic refractors for planetary work...   John Allseits

[maadscientist]

Planetary imagers (including myself) use the C14 SCT as the defacto standard. MCT's get radically expensive above 8, 9 inches. Refractors are not really in the game.

 

"Is the best way to compare them by starting at price you can afford and target audience of sky goal?" YES

[Jon Isaacs]

Planetary imagers (including myself) use the C14 SCT as the defacto standard. MCT's get radically expensive above 8, 9 inches. Refractors are not really in the game.
 
"Is the best way to compare them by starting at price you can afford and target audience of sky goal?" YES

A few planetary imagers use larger Newtonian, Anthony Westley who discovered a comet impact on Jupiter in 2009 uses a 14.5 inch home built Newtonian.

http://www.skyandtel...rs-bird-strike/

https://en.m.wikiped.../Anthony_Wesley

https://jupiter.samb...thonyWesley.jpg

Jon

[rolo]

For planetary imaging I prefer the aperture advantage of the C14. For visual planetary views I prefer the superior sharpness and contrast of the Intes 10" f/12.5 Mak-Cass.You could buy two C14 for the price of one 10" Mak Cass, though.

[Ptkacik]

What about color correction? Why is it a refractor thing?

 

Since the light doesn't pass through glass, a Newtonian would be perfect. But it does have glass in the eyepiece.

 

SCT's and MCT's don't seem to have it but the light enters through glass. In the case of the MCT, the light enters at an angle that looks greater than in a refractor.

 

I had a 110mm Orion "Apo" refractor and on Venus it had a strong violet halo that I've not seen in my Cassegrains. 

 

Clear skies,

Peter

[GJJim]

Russian MCTs are available with f/10 focal ratios comparable to SCTs.

 

There is more to color error and correction than simply having glass in the path of incoming light. In MCTs and SCTs the corrector lens is optically weak compared to the lenses in a refractor, and the correctors use carefully tailored thickness and refractive index to minimize the error.

[vahe]

 

2. An MCT is higher power tool with an F15 to F20 ratio. Great high power optics.

 

 

MCT’s come in all sizes and all F ratios, f/6 to f/20, you can choose what best suits your needs, currently Russian Maks in all sizes up to 16” are available in f/10 version with about 30% CO.
For those mainly interested in high power planetary observation most larger Russian Maks are also offered in f/15 version with somewhat smaller CO. somewhere around 27%
F/20’s are unusual breed, these are optimized for highest contrast with 22% CO, currently OMC offers 8” f/20, in the recent past TEC offered f/20’s in 8” and 10” sizes.
All compound telescopes that are made of refractive and reflective elements will have CA, no way around that, but just how much CA is in high end Maks? According to Yuri the amount of CA in his Maks is an order of magnitude less than the finest apochromats, in another words visually they are color free.

 

Vahe

[azure1961p]

When both Cassegrain  systems are well made both give terrific crisp images.  Doublestars are cut clean and true.  The advantages with the mak (from all I've read)  is that since all the surfaces a spherical it's easier to fabricate them to a higher degree of correction.  Too,  the longer focal lengths of the mak allow for a smaller central obstruction. Inch for inch of aperture maks produce a better sharp contrast image... Again so I've read, but I believe it too.

 

My thoughts on it are this:

 

If you want the sharpest images of planets get the biggest SCT you feel comfortable using and can afford.   The post processing of ccd images is so extremely effective (even ruthless)  even with the large CO  and perhaps optics not quite as corrected as a maks ,  the resulting images will be dazzling. 

 

The mak is an excellent imager too but it's refined subtleties might best be appreciated visually.  And visual in nothing to sneeze at.  CCDs aside there is still no electronic medium that records the fidelity of the high resolution image we see through a fine scope.  There's a tenuous nature that CCDs plow through without acknowledging it. 

 

 

Give you a good example.  I'll be imaging Jupiter with my 8" f9 reflector with its 16% CO this winter.  It's a wonderful visual instrument,  but an image shot through a C8  by a good imager will leave you wondering what the he- -  the big long scope was for.  Post processing can be that aggressive. 

 

 

After you answer your portability questions and costs you might want to float whether or not you are visual or ccd.  If it's both than the SCT might be your best bet.  If it's staunchly visual you may prefer the the mak. 

 

 

Again,  both designs,  we'll made,  produce terrific meaningfully beautiful images.  Where your core interests lie  maybe your best compass. 

 

Pete

[Bomber Bob]

After you answer your portability questions and costs you might want to float whether or not you are visual or ccd.  If it's both than the SCT might be your best bet.  If it's staunchly visual you may prefer the the mak.

 

Since it's an either / or choice, I'd go with the SCT over an MCT - you'll get more aperture for the same money.  SCTs are the "all'rounder" portable solution, good at lots of different things.

[Darren Drake]

 

 

2. An MCT is higher power tool with an F15 to F20 ratio. Great high power optics.

 

 

MCT’s come in all sizes and all F ratios, f/6 to f/20, you can choose what best suits your needs, currently Russian Maks in all sizes up to 16” are available in f/10 version with about 30% CO.
For those mainly interested in high power planetary observation most larger Russian Maks are also offered in f/15 version with somewhat smaller CO. somewhere around 27%
F/20’s are unusual breed, these are optimized for highest contrast with 22% CO, currently OMC offers 8” f/20, in the recent past TEC offered f/20’s in 8” and 10” sizes.
All compound telescopes that are made of refractive and reflective elements will have CA, no way around that, but just how much CA is in high end Maks? According to Yuri the amount of CA in his Maks is an order of magnitude less than the finest apochromats, in another words visually they are color free.

 

Vahe

I have both the 6 and 8 inch TEC maks and can attest to them both being virtually color free even under the highest level of testing .

[rmollise]

What are the differences between a Maksutov Cassegrain (MCT) and a Schmidt Cassegrain (SCT) or any thing else? Is the best way to compare them by starting at price you can afford and target audience of sky goal?

1. Not true at all. SCTs can display very good contrast. I'm assuming you've never used a collimated SCT in steady seeing on a planet?

2. Power is a function of the eyepiece. An SCT can deliver the same magnifications. the benefit of the longer focal ratio systems is that it's easier to reach higher power with longer focal length eyepieces, which tend to be more comfortable to use.

3. Not sure what you're trying to say...and I thought the subject was MCT vs. SCT.

4. Yep. They are big, and don't offer substantial enough advantages over the other two designs to ensure they are very popular.

[Darren Drake]

I have compared many times a high quality C8  on saturn to a 7 inch mak newt.  While the view through the C8 was very good to the extent that no one would say anything  negative about the view the mak newt clearly would give a better more contrasty and more color accurate  view.   Even untrained eyes would see the difference at the astronomy camp I  run each summer.  

 

In the upcoming days I plan to compare my 3 C8s to the 6 and 8 inch TEC maks I have recently come into.  My goal is to see if I can sacrifice the one C8 I use at the astronomy program I run in the summers for the 6 inch Tec mak for planetary viewing....

 

Edited by Darren Drake, 01 November 2015 - 11:17 AM.

[Daniel Mounsey]

More commonly SCT's are fine for general observation but nothing special at any particular thing except low cost and portability.

[PowellAstro]

And comfort, minimal upkeep, super views(when collimated properly), size per inch, mounting requirements.........

[orion61]

Some of the best Planetary Photos were from Donald Parker, a dedicated Newtonian user that was a huge inspiration for myself and many others to get into Astrophotography.

I think one difference is Mak Optics are a bit easier to produce up to a certain size. It took me awhile to realize a lot of the differences between the sharpness and the way the Airy Disks look between the two is the lower optical quality of Schmidts

on average with 1/4 wave optics or worse. against 1/8th wave Maks. IF the optical quality is the same, the Star Tests should look virtually the same, with the difference of a slightly thicker first diffraction ring in the SCT due to a larger Central obstruction thus less energy in the Airy Disk itself.

I didn't believe it myself, and I bought into the company claims of 1/8th or 1/10th wave optics of the Schmidts. Yes optical components can have 1/8th wave figure with the scope as a whole having well under 1/8th wave.

SOME models like the Original Celestron Ultima/PowerStar, and Compustar, hit the high mark more constantly.

but early Meade 8 and 10", and Dynamax 8" and 6" didn't fair so well, (an understatement in some).

The standard of quality is with Damian Peach and his superb C14 from what I have seen lately.

[Daniel Mounsey]

Don was a mentor to many, however, planetary imaging says little to nothing about the optical quality of telescopes. That's nearly all just conditions for good data, a good camera combined with great processing.

[maadscientist]

 

Planetary imagers (including myself) use the C14 SCT as the defacto standard. MCT's get radically expensive above 8, 9 inches. Refractors are not really in the game.
 
"Is the best way to compare them by starting at price you can afford and target audience of sky goal?" YES

A few planetary imagers use larger Newtonian, Anthony Westley who discovered a comet impact on Jupiter in 2009 uses a 14.5 inch home built Newtonian.

http://www.skyandtel...rs-bird-strike/

https://en.m.wikiped.../Anthony_Wesley

https://jupiter.samb...thonyWesley.jpg

Jon

 

Yes, Anthony Wesley, referred  to as "Bird" images with his customized newtonian. Back in the day, when Registax was just hitting stride, he developed his own sotrting algorithm. He didn't like the results he got using the Registax options, so he made his own....

 

Bird also hit the lottery TWICE....catching impacts on Jupiter live. My buddy Rich Jakiel was the last imager to report before the big impact that ripped the gas for about  week, where they turned Hubble to it....in his lectures, he refers to this as the ultimate booby prize....I ended up being the 4th or 5th imager to submit my Jupiter to BAA and ALPO after the news hit....

 

Bird has had to make some modifications to his dob, as usually there is not enough in focus to use a filter wheel and mono camera in a traditional setup. However, one can use a one shot color planetary camera with an off the shelf newt...

 

I have a 20 inch Starmaster with which I planetary image off an EQ platform....it works well, but I do run into temp acclimation issues with the large mirror.....Seeing also is the limit, so generally it will give me no better resolution than the C14, although I am hoping I can break through this season with Mars and Jupiter.

[maadscientist]

Some of the best Planetary Photos were from Donald Parker, a dedicated Newtonian user that was a huge inspiration for myself and many others to get into Astrophotography.

I think one difference is Mak Optics are a bit easier to produce up to a certain size. It took me awhile to realize a lot of the differences between the sharpness and the way the Airy Disks look between the two is the lower optical quality of Schmidts

on average with 1/4 wave optics or worse. against 1/8th wave Maks. IF the optical quality is the same, the Star Tests should look virtually the same, with the difference of a slightly thicker first diffraction ring in the SCT due to a larger Central obstruction thus less energy in the Airy Disk itself.

I didn't believe it myself, and I bought into the company claims of 1/8th or 1/10th wave optics of the Schmidts. Yes optical components can have 1/8th wave figure with the scope as a whole having well under 1/8th wave.

SOME models like the Original Celestron Ultima/PowerStar, and Compustar, hit the high mark more constantly.

but early Meade 8 and 10", and Dynamax 8" and 6" didn't fair so well, (an understatement in some).

The standard of quality is with Damian Peach and his superb C14 from what I have seen lately.

Don Parker was "The Bomb"!!! The amount of struggle he went through in the days of film boggle the mind....his dedication to the craft was simply "the best". We had him up to the Peach State Star Gaze as a featured speaker and he was brilliant...one of his best qualities was his ability to laugh and make everyone else laugh. In a hobby that gets a little dry, this guy could have you rolling on the floor.....we nicknamed him "The Ancient One" at the ALPO convention... is and will be sorely missed.

 

On the optics of the Schmidts, I have found them to be good, near the quarter wave for total throughput evaluation. One thing to keep in mind is collimation, temp acclimation, and seeing are variables that are unknown when discussing scopes online....too much variability to give any form of metrology.

[Darren Drake]

I will be having some fun tonight once again comparing 2 maks and 2 C8s and a newt.  Also later an Eon 120 will be added to the mix.  I only have so many mounts lol.

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[A6Q6]

The first photo is unprocessed but shows the seeing that night. The second is the same photo  processed with RigiStax 6 . I used a Quantum 6 Mak 33% CO, that I have had since 1978 and an old Orion StarShoot imager III camera.   I would rather observe than image but on a poor night I can get pretty good results imaging because I can stack fleeting moments.   My Mak has never taken a back seat to any SCT in over 35yrs until I got a mint 30yr old Super C8 Plus last summer.  I used to laugh years ago when I read Celestron had 1/10 wave optics. I'm not laughing anymore.  Since this SCT can run with my Mak,(big CO and all) the advantage is 8" vs 6" and it is much lighter than the 6" Mak.  They say Celestron SCTs are lighter than the same size Meade.   I will leave the reflector, both dob and eq mounted to others, although I have a C5 with very good optics that I would take over the wonderful RV-6 that I had years ago because the C5 is sooooo easy to move around.   I don't have any experience with large refractors but I am enjoying a 60mm mounted on my new to me C8 for its low power wide field views. 

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Edited by A6Q6, 01 November 2015 - 08:05 PM.

[A6Q6]

 My Quantum 6 Mak.  The C8 is just as sharp as the Mak.

A small refractor is great on the C8 for low power wide field views.

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Edited by A6Q6, 01 November 2015 - 07:56 PM.

[maadscientist]

Don was a mentor to many, however, planetary imaging says little to nothing about the optical quality of telescopes. That's nearly all just conditions for good data, a good camera combined with great processing.

Daniel,

 

What's up? When are you going to invite me to speak out west? (brown nosing times 10).....

 

Your post gave me pause to reflect on optical quality as it manifests in observing vs imaging.....basically I probably disagree more than agree with your statement, but it's close....

 

I would differentiate by saying raw aperture overcomes optical quality for planetary imaging over around 8 inches. Meaning the optical quality can slide a bit, but is compensated for by the inherent resolving power gain. However, I would put an asterisk on that by saying there is a limit to the optical degradation allowed and that would be no less than 1/3 wave....a 1/2 wave optic will just not do it....I have no hard scientific evidence to back this up except I have looked through over 100 SCT's and imaged with a bunch and have compared a lot of images with known optical quality reports...so you are probably correct in your statement for large optics....

 

To flip the other side, I would say smaller optics with high quality do show up with better performance at the eyepiece, and somewhat less in imaging. Any loss of energy from the airy disk has a greater percentage impact over the area of the optic. Nonetheless, it's a fine line, and long exposure, whether its a 2-5 minute video or 5 minute sub, does allow enough signal to be manipulated pretty heavy in software.

 

So I would probably say that there are really 2 standards for optics....visually, where the eye acts like a video camera and smooths out the blur, disallowing fine fine details, and imaging, where those fleeting moments are captured, bottled, and distilled to a high resolution image...

 

My 2 cents...

 

Dan Llewellyn

"The Rodney Dangerfield of Planetary Imaging"

[Bill Barlow]

Darren and A6Q6,   I recently compared my TEC 6 to my very good optically LXD75 Meade ACF.  I found that the Meade beat the TEC noticeably on deep sky objects but they were pretty close on splitting some closer double stars similar to Izar.  But the Meade cost about 4X less than the TEC.  But I still like views through the TEC a lot.

 

Bill

[Ptkacik]

So what makes a Maksutov so much sharper than a Schmidt?

 

In a shootout, my 7" Mak easily beat out my 8" SCT. I still like the lighter weight SCT but at these sizes, I can carry either one easily. I had aperture fever and can say that at larger sizes, I don't like to carry any telescope, (but still do).

 

To answer two earlier questions, I am strictly visual. I also spend lots of time collimating. On my 16" Dob, I use a TuBlug and collimate on every object. I use an artificial star for my  Cassegrains.

 

So what is it about the Mak that makes it so good? And in a similar tone, what is it about Dall Kirkhams or iDK's that make them so sensitive to temperature, (or is it that their owners are just that much more sensitive)?

 

Clear skies,

Peter